Abstract: A method is performed by a server for searching for information contained in encrypted data without revealing the information to the server. The server receives from a client: an encrypted matrix containing the information to be searched for in files and linking the information to the files; for each of the files, a merged secret key; and an encrypted vector having a length corresponding to a number of the information. The encrypted data is evaluated by performing a multiplication of the matrix with entries in the vector using a multikey homomorphic encryption scheme. For each of the files, a value of the multiplication of the matrix is decrypted using the corresponding merged secret key so as to determine which of the files contains the information. The files containing the information are sent to the client.

Abstract: A method is performed by a server for searching for information contained in encrypted data without revealing the information to the server. The server receives from a client: an encrypted matrix containing the information to be searched for in files and linking the information to the files; for each of the files, a merged secret key; and an encrypted vector having a length corresponding to a number of the information. The encrypted data is evaluated by performing a multiplication of the matrix with entries in the vector using a multikey homomorphic encryption scheme. For each of the files, a value of the multiplication of the matrix is decrypted using the corresponding merged secret key so as to determine which of the files contains the information. The files containing the information are sent to the client.

Abstract: A method for providing encrypted data for searching of information includes generating a number of distinct key triples each comprising a public key, a corresponding secret key, and a corresponding evaluation key based on searchable information and files to be searched. Information indicating whether the searchable information is included within the files is encrypted with a key of the generated key triples. The secret keys are merged to obtain a single secret key for an entirety of the searchable information within respective ones of the files for each of the files. The encrypted information is provided with the merged secret keys for each of the files as encrypted data for searching of information within the files. The generating of the distinct key triples and the encrypting of the information are performed based on a multikey homomorphic encryption scheme.

Abstract: A method and system for modifying an authenticated and/or encrypted message by a modifying party exchanged between a sending party and a receiving party based on a secure communication protocol, the method includes the steps of a) dividing a clear message into non-modifiable parts and modifiable parts by the sending party; b) including modifiable part information into the message by the sending party; c) authenticating and/or encrypting the message by the sending party; d) providing en- and decryptability and/or authenticability of the message to the modifying party in such a way that the modifying party can only modify the modifiable parts of the message; e) modifying one or more modifiable parts by the modifying party; and f) providing an authenticated and/or encrypted modified message according to the secure communication protocol to the receiving party.

Abstract: A method for providing encrypted data for searching of information includes generating a number of distinct key triples each comprising a public key, a corresponding secret key, and a corresponding evaluation key based on searchable information and files to be searched. Information indicating whether the searchable information is included within the files is encrypted with a key of the generated key triples. The secret keys are merged to obtain a single secret key for an entirety of the searchable information within respective ones of the files for each of the files. The encrypted information is provided with the merged secret keys for each of the files as encrypted data for searching of information within the files. The generating of the distinct key triples and the encrypting of the information are performed based on a multikey homomorphic encryption scheme.

Abstract: A method and system for modifying an authenticated and/or encrypted message by a modifying party exchanged between a sending party and a receiving party based on a secure communication protocol, the method includes the steps of a) dividing a clear message into non-modifiable parts and modifiable parts by the sending party; b) including modifiable part information into the message by the sending party; c) authenticating and/or encrypting the message by the sending party; d) providing en- and decryptability and/or authenticability of the message to the modifying party in such a way that the modifying party can only modify the modifiable parts of the message; e) modifying one or more modifiable parts by the modifying party; and f) providing an authenticated and/or encrypted modified message according to the secure communication protocol to the receiving party.